You can't enter an international phone number in the Mailing Address & Phone number section containing personal information. The IRS will not call an international phone number.
You can enter the phone number of a relative or friend in the U.S,, or a "dummy number" (800-555-1212). This will allow you to complete your return, and the IRS will identify your entry as a placeholder number - if they have questions, they will mail them to you.